Macrolide antibiotic resistance and production in Streptomyces narbonensis

Narbomycin, a macrolide antibiotic produced by Streptomyces narbonensis, consists of a 14-atom polyketide to which the deoxyhexose sugar, desosamine, is attached. The aim of this study was to identify the desosamine biosynthetic gene cluster.;In Streptomyces there is a tendency for genes concerned with the same biochemical pathway to be grouped together in clusters. These biosynthetic gene clusters are often associated with genes conferring resistance to the antibiotic in the producing organism. The relationship between the resistance genes and the biosynthetic genes has been of great importance in studying antibiotic biosynthesis, since a number of biosynthetic clusters have been isolated using the corresponding resistance gene as a probe against cosmid libraries.;Two resistance determinants have been cloned from S. narbonensis, nmr A and nmrB. The nucleotide sequence was determined and both genes appear to encode 23S rRNA methyltransferases conferring MLS resistance.;A cosmid library of S. narbonensis DNA was constructed and probed with the narbomycin resistance genes. This led to the isolation of the narbomycin biosynthetic gene cluster. Mycaminose genes from the tylosin biosynthetic gene cluster of S. fradiae were also available as probes and were used in hybridisation analysis against the S. narbonensis cosmid library; leading to the identification of putative desosamine genes and a preliminary map of the narbomycin biosynthetic gene cluster.